Battery Backup

[123.Shawn T.W.]

Respironics tech told me on the phone that MSW invertors (300w) were fine.

[TalonNYC]

What percentage of users here use some form of battery backup? For those who are, what do you consider the best? What is your primary use, power loss prevention, camping?

I have a small APC Uninterruptible Power System (UPS) that I plug the CPAP system and my alarm clock into. I use it because my neighborhood has a bad history of losing power for up to 24 hours about once a year on average. The one I use is one of APC's very basic models designed for allowing computing systems to keep working during a power failure, and it's been pretty good so far. We've had one outage since I got it, and I slept right through it. Seeing the data the next AM, it appears that the machine itself didn't even notice the outage at all =)

[archangle]

Respironics tech told me on the phone that MSW invertors (300w) were fine.

Unfortunately, they don't seem to have published this info anywhere. Is it OK for just the blower, or for the blower plus humidifier, for PRS1 units, or also for M series, and the legacy models as well?

I would expect the PRS1 units and humidifiers would be OK.

The problem with ResMed is the model machines where the humidifier is powered off of AC power. Legacy Resmed and some M series humidifiers are AC powered.

[archangle]

I have a small APC Uninterruptible Power System (UPS) that I plug the CPAP system and my alarm clock into. I use it because my neighborhood has a bad history of losing power for up to 24 hours about once a year on average. The one I use is one of APC's very basic models designed for allowing computing systems to keep working during a power failure, and it's been pretty good so far. We've had one outage since I got it, and I slept right through it. Seeing the data the next AM, it appears that the machine itself didn't even notice the outage at all =)

Do you have any idea how long the power was off? I wouldn't expect most UPSs to run a CPAP for very long.

[TalonNYC]

Do you have any idea how long the power was off? I wouldn't expect most UPSs to run a CPAP for very long.

The home versions won't. One small step up however, and you should get at least 4 hours out of it. In my case, the power was out for about eight, but since it happened overnight, I woke up before the juice ran out.

[Burkebang]

I just had an idea for a CPAP battery backup system. I am an amateur photographer and I also use my jumpstart battery as a power source for my studio flashes when I don't have power available. I do this via a pure sine inverter. But there is also very good batterysystems for flashes that you can buy off the shelf.

Paul C Buff makes a very nice product called the Vagabond Mini. This product has a high quality pure sine inverter in it. The specs tells me that it should be good enough to power any CPAP for a night. I think the price is very good, considering you get a battery, pure sine inverter and separate quick charger. Add an extra battery and most people should have all they need at a good price. This should be specially attractive for Resmed machines and others that don't accept 12 volt directly.

They may still have some Vagabond II's also, this product has a 20 amp sealed lead acid battery, while bigger and less portable, it should power a CPAP for 3 nights without recharging.

These products are highly regarded by photographers and are used by pro's.

http://www.paulcbuff.com/vagabond.php

[archangle]

I understand pure sine inverters are usually less energy efficient than MSW, so a pure sine wave inverter is not necessarily better. The inefficiency is especially bad at low power levels.

I presume efficiency varies a lot between different models.

[123.Shawn T.W.]

Respironics tech told me on the phone that MSW invertors (300w) were fine.

Unfortunately, they don't seem to have published this info anywhere. Is it OK for just the blower, or for the blower plus humidifier, for PRS1 units, or also for M series, and the legacy models as well?

I would expect the PRS1 units and humidifiers would be OK.

The problem with ResMed is the model machines where the humidifier is powered off of AC power. Legacy Resmed and some M series humidifiers are AC powered.

I only enquired about the 550 & 560 models, as that is what I have ...

[ColinP]

I keep a deep cycle battery next to my bed, and I have a home-made DC cable which plugs directly into my Resmed's 12V socket. The humidifier doesn't work when I'm on battery power but that doesn't worry me too much, I only bother with the humidifier a few times each winter anyway.

[DiverCTHunter]

They may still have some Vagabond II's also, this product has a 20 amp sealed lead acid battery, while bigger and less portable, it should power a CPAP for 3 nights without recharging.

These products are highly regarded by photographers and are used by pro's.

http://www.paulcbuff.com/vagabond.php

I think you're being overly optimistic, because my absolute best-case calculations put it closer to 2-2/3 nights without the humidifier.

Let's do the math for a pie-in-the-sky best case:

• Assume a theoretically perfect 12VDC 20 Amp/Hour battery. 12V x 20Ah = 240Wh of power.
• Assume that the Pure Sine Wave inverter is 80% efficient (realistically more like 75%). 240Wh x .8 = 192Wh that the PS1's brick can use.
• Assume that the PS1's brick is 90% efficient (realistically more like 80%). 192Wh x .9 = 172.8Wh left for the machine. For the sake of theoretical perfection, we'll round this up to 173.
• Experimentally, I've found that the PRS1 550 draws approximately 2 watts in standby mode, 40 watts with the humidifier in preheat mode, 11-14 watts with the blower at full blast and no resistance on the air circuit, and 5-8 watts with exhale pressure on the air circuit.
• Assume a 1:1 inhale to exhale ratio (Sleepyhead shows mine was 2:1 while in a sleep stage, but again, we're calculating a best case scenario). avg(11W,5W)=8W
• 8W x 8h = 64Wh/night
• 173Wh / 64Wh/Night = 2.7Nights to 100% depth of discharge

I don't have enough time to do the real world calculations before I head to work at the moment, but I think you get the picture.

[ColinP]

Not only that, but if you're discharging your battery to fully discharged, it is not going to last very many recharge cycles before it fails. Even deep cycle batteries shouldn't be taken much below 50% charge.

[DiverCTHunter]

Not only that, but if you're discharging your battery to fully discharged, it is not going to last very many recharge cycles before it fails. Even deep cycle batteries shouldn't be taken much below 50% charge.

And you have to take care not to overcharge or overheat an SLA or AGM battery or you'll lose electrolyte and kill the battery even faster than over-discharging alone will.